What is the final product of following reactions ?
`Hex-3-"ynal" underset((i) PBr_3 , (ii) Mg//"ether",(iii) CO_2//H_3O^(+))overset((i) NaBH_4)to`

Options

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Answer

To determine the final product of the given reactions starting from hex-3-ynal, we will follow the steps outlined in the problem.

### Step-by-Step Solution:

1. **Identify the Structure of Hex-3-ynal**:
- Hex-3-ynal has the structure:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{CCHO} \]
- This means it has a triple bond between the third and fourth carbon atoms and an aldehyde functional group.

2. **Reaction with PBr₃**:
- The reaction of hex-3-ynal with PBr₃ will convert the aldehyde (-CHO) group into a bromide (-Br) through a nucleophilic substitution reaction.
- The product after this step will be:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{CCH}_2\text{Br} \]

3. **Formation of Grignard Reagent**:
- Next, we react the bromide with magnesium (Mg) in ether to form the Grignard reagent. The Grignard reagent will be:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{CCH}_2\text{CH}_2\text{MgBr} \]

4. **Reaction with CO₂**:
- The Grignard reagent will then react with carbon dioxide (CO₂). The carbon atom of the Grignard reagent will attack the electrophilic carbon of CO₂, leading to the formation of a carboxylate intermediate:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{CCH}_2\text{COO}^- \]

5. **Protonation of the Carboxylate**:
- Finally, we will protonate the carboxylate ion using H₃O⁺ (acidic workup). This will yield the final product, which is a carboxylic acid:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{CCH}_2\text{COOH} \]

### Final Product:
The final product of the reaction sequence is:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{CCH}_2\text{COOH} \]